The invention relates to “active implantable medical devices” as defined by Directive 90/385/EEC of 20 Jun. 1990 of the Council of the European Communities, specifically implants to continuously monitor heart rhythm and deliver if necessary to heart electrical pulses for stimulation, resynchronization and/or defibrillation in case of rhythm disorder detected by the device. The invention more particularly relates to devices for treating heart failure (HF), as an alternative or in addition to the treatment of cardiac rhythm disorders.
This therapy is designed to resynchronize the contraction of the heart chambers (atrium and ventricle, and between the two ventricles) so as to improve the patient's condition by optimizing the phases of the hemodynamic cycle. The cycle includes pre-ejection, isovolumetric contraction, systolic ejection, isovolumetric relaxation and finally filling of the cavity.
Most of these devices implement a technique called “CRT” (Cardiac Resynchronization Therapy) or “BVP” (Bi-Ventricular Pacing) for delivering electrical pulses as necessary to ensure joint and continuous stimulation of the two ventricles, left and right, to resynchronize them. This biventricular resynchronization technique however addresses only one of the forms of heart failure, known as “systolic failure”. In this form of the disease, the heart muscle is unable to provide the force necessary to ensure adequate cardiac output, and the patient shows signs of expansion resulting in a delay of left ventricular depolarization. CRT Biventricular pacing is then used to resynchronize the ventricles and make cardiac contraction more uniform.
In the other form of heart failure called “diastolic failure” or “preserved ejection fraction heart failure” (HFpEF, Heart Failure with preserved Ejection Fraction), there is no desynchronization of the ventricles; it comes from a failure in the left ventricular filling. Biventricular CRT stimulation will be ineffective in this case. But this condition affects about 40% of heart failure patients, and there is no known effective treatment to remedy to it.
This form of disease in some patients may be the result of a disorder of conduction in the atria (inter-atrial block), which delays the depolarization, and therefore the contraction of the left atrium (OG) with respect to the right atrium (OD). However, as atrioventricular conduction pathways are not altered, depolarization and contraction of two the right (VD) and left (VG) ventricles occur within a reasonable time, without synchronization VD-VG. It is between the contraction of the left atrium and that of the left ventricle that the inter-atrial block OD-OG generates a poor sequencing OG-VG. The delay of the contraction of the left atrium has for consequence that it contracts substantially at the same moment as the left ventricle, and therefore cannot properly fulfill its function and contribute to the left ventricular active filling.
To treat this heart failure with preserved ejection fraction and pathology, a technique of atrial overdriving including stimulating the left atrium to a frequency slightly above the spontaneous sinus rhythm frequency (i.e. the rate of the right atrium) has been proposed, thereby systematically causing premature depolarization of the left atrium and thereby restoring a more normal OG-VG sequence.
Specifically, in this known technique, the device regularly measures the spontaneous rhythm of the patient and applies a sequence of pacing pulses at a slightly faster rate, arbitrarily programmed to cause a prematurity in the order of 50 to 100 ms compared to an atrial coupling interval corresponding to the spontaneous sinus rhythm. After several cycles at this accelerated pace, the frequency gradually slows until reappearance of spontaneous activity, then the overdriving method is repeated in the same way and so on.
The applied stimulation frequency thus varies continuously between values wherein it is too fast (overdriving period) or too slow (period of reappearance of spontaneous rhythm, with OD-VD synchronization), without real monitoring of the effectiveness of a possible return to a proper synchronization of the left cavities.
This pacing mode may also interfere with the filling of the right cavities. In fact, due to premature stimulation of the left atrium, the OD-VD synchronization is significantly altered in a manner which may be incompatible with satisfactory filling of the right ventricle (these aspects will be clarified in the detailed description). Improvement therapy in the left ventricular filling is thus likely to induce adverse effects on the filling of the right ventricle, so in the cavity that was not affected by the pathology to be treated.
Another technique is described in EP 2471575 A1 (Sorin CRM SAS) which, in particular to overcome these drawbacks, implements a sensor for collecting a endocardial acceleration signal (EA). The EA signal is analyzed to detect the presence of a specific component reflecting the atrial contraction (EA4 component) and to identify the moment of occurrence of this component. If the EA4 component is present, this means that the sequencing of atrial contractions is correct because otherwise (left atrial contractions too late), the EA4 component would be masked in the component of the EA signal corresponding to the immediately following ventricular contraction (EA1 component). The inter-atrial stimulation interval (AA interval) is then dynamically adjusted depending on the result of this analysis. However, this technique requires an implantable lead provided with an implanted endocardial acceleration sensor, and a generator capable of processing the signals delivered by such an EA sensor.
A similar technique is disclosed by U.S. Pat. No. 8,583,234 B1, which proposes in addition, after a first cardiac cycle without left atrial pacing, to deliver an overdriving pulse during a second immediately consecutive cardiac cycle.
The exemplary embodiments herein propose a technique for treatment of heart failure with preserved ejection fraction in patients with inter-atrial mechanical delay, which overcomes the drawbacks of the methods proposed so far and which does not require the use of means for collecting and analyzing an EA signal.
Exemplary embodiments also propose a technique that ensures recovery of diastolic function in a method that is simple (in terms of resources used) and very reactive (efficiency obtained cycle to cycle), allowing the patient to recover a satisfactory OG-VG sequencing (sequencing of left atrial contraction relative to that of the left ventricle), so that the atrium can correctly perform its filling function completion for the left ventricle.
Exemplary embodiments are directed to a conventional dual chamber device (with left atrial detection/stimulation and ventricular detection, but without detection of depolarization signals of the right atrium), and this simply by reprogramming the control circuits of this device (e.g., without hardware modification).